Anyone who has ever seen fireflies do their luminescent mating dance on a summer’s night has wondered: How do they light up like that? Now, two researchers, Sara Lewis from Tufts University and Thomas Michel from Harvard Medical School, have unraveled the mystery. Fireflies produce their light with nitric oxide, which is the same gas that regulates blood pressure in humans. The effect of Viagra in humans is also due to nitric oxide. Lewis and Michel, who are married to each other, have been discussing their individual research interests since they met each other as undergraduates at Harvard. Their research overlapped when they realized that they were both working on biological processes involving nitric oxide.